Network timing

This release adds support for recording request timings:

client.request({ timing: true }).then(response => {
    console.log(response.timings);
    /* {
           socket: 10,
           lookup: 30,
           connect: 60,
           response: 100,
           end: 150
      } */
    console.log(response.timingPhases);
    /* {
           wait: 10,
           dns: 20,
           tcp: 30,
           firstByte: 40,
           download: 50,
           total: 150
      } */
})